On a known filter assembly machine, first elongated members, each defined by a double cigarette portion, are each cut transversely by a first cutting unit into two single portions; the single portions are then parted axially, are separated by a double filter, and are connected to each other and to the filter by a gummed band to form a double cigarette, which is cut transversely at the filter by a second cutting unit into two single filter-tipped cigarettes.
At each cutting unit, the cigarette portions are supplied transversely (i.e. in a direction perpendicular to their longitudinal axis) by a conveyor drum fitted with a circular blade rotating at high speed. To ensure a clean cut at all times, each cutting unit is fitted with a sharpening device, e.g. of the type described in U.S. Pat. No. 4,497,143-A1, for maintaining a keen blade edge. In view of the high output speeds of modern filter assembly machines (as many as 20,000 cigarettes a minute), continual sharpening subjects the circular blades of the cutting units to severe wear, thus requiring frequent replacement. In particular, the circular blade of the first cutting unit wears out faster than that of the second, by cutting the cigarette portions at the tobacco, whereas the circular blade of the second cutting unit cuts the cigarette portions at the filter material, which on average is softer and more homogeneous than tobacco.
In a high-speed, last-generation filter assembly machine capable of producing up to 20,000 cigarettes a minute, the circular blade of the first cutting unit must be changed at the end of each shift, i.e. every 8 operating hours. And since this calls for skilled labour and involves a certain amount of downtime (5-10 minutes), the frequency with which the circular blade of the first cutting unit must be changed obviously increases cost, in terms of both labour and downtime production loss.